A HIGHLY SENSITIVE OPTICAL-DETECTOR FOR USE IN DEEP UNDERWATER

We have developed an optical detector module for use in deep underwate r experiments that will search for high-energy neutrinos from cosmic r ays and astronomical sources. This module is sensitive to single photo ns, is operable under high pressure, functions automatically and is re motely controlled. The optical module is based on a 15 in, diameter ph otomultiplier tube (PMT), with control and read-out electronics mounte d inside a 17 in. diameter glass pressure housing. The photomultiplier output signal is converted into two optical pulses by the electronics , one giving the hit time and time-over-threshold of the PMT output pu lse and the other giving the charge-integrated PMT signal. Information on the arrival time and intensity of light can be extracted from thes e pulses. The time jitter of the optical modules is similar to 6 and s imilar to 2 ns at FWHM for one photoelectron and similar to 100 photoe lectrons, respectively. The unit requires 10 W power delivered at 48 V DC on a line with superposed bidirectional control signals. Fast outp ut is uni-directional on a multi-mode fiber optic link to a remote tim e digitizer. The module has been successfully tested and calibrated in the laboratory, and several have briefly operated in the deep ocean. (C) 1998 Elsevier Science B.V. All rights reserved.